The Trace
by dhasenan
Summary: Simple concepts never have a straightforward execution.


It was pure luck, Melina reflected, that had gotten a Muggleborn like her this job as an enchanter at the Ministry. It was her name; the Gaunt family was – well, not well-respected, but at least known. And with the number of people unwilling to give jobs to anyone without the right surname, that put her right at the lead.

Pure luck; but she hadn't yet determined whether it was good luck or bad. She was assigned the task of enchanting the whole of the island with something that would inform the Ministry of underage magic use. "Children are getting up to all sorts of nonsense," Richard Lothian in the Magic Reversal Squad told her gruffly, "and it's causing nine kinds of hell when we're not finding it for weeks. Rune us up something, will you?"

She'd had to cross-reference eigenvectors for 6x12 complex matrices with the Norse _and_ Phoenician rune series, and some of the numbers she crunched didn't even show up in Rodson's Compendium of Enchanting Structures. She'd spent over a week calculating the exact position and orientation of each rune. And then it had taken another week to double check her work. And then a _third_ week to redo it all from scratch with a NEWT student who had secured a summer job checking her along the way, when she'd gotten different results the first two times.

But fortunately the first and third results _mostly_ agreed, and she'd tracked down the mistakes, and the final result had only taken six hours to carve with young Omoye's help. She called the result The Trace, with audible capital letters. She'd activated it, set it up in the Reversal Squad's office, and called it a day.

The next day, the granite plinth was back in her office with a note on it: "The Magic Reversal Squad does not need to be called upon to Obliviate people in Diagon Alley."

"Fuck," Melina said. Omoye nodded. "Okay, let's take a look. We set it up to go the full range of the island, adjacent land and all, how do we get it to exclude Diagon Alley?"

"The wards," Omoye said instantly. "Diagon Alley has Muggle-repellent wards. So does Hogwarts."

"Hogwarts, yes, I can't believe I forgot that. I need coffee."

"Coffee hasn't been invented yet," Omoye reminded her, "it's 1412. But you can move to Yemen and be among the first to drink it in a few decades."

"Tea?" Melina asked hopefully.

"We have tea -"

"Yay!"

"If you want to travel to China to drink it."

"Damn. It's going to be a long day."

"Back to work, boss?" Melina nodded. "Okay, I think we just need to multiply this submatrix by the manachaen root for the ward, right?"

"Ye—no, that depends on the ward. And that will get a _lot_ of types of wards, not just Muggle repellents. And it only works if-"

"If the ward's Crawley-isomorphic, right," Omoye completed for her. "Otherwise they'll cancel out partially and you'll get interference patterns, right?"

"Right. Are you sure you don't want to work with me after you graduate?"

Omoye shook her head. "I can't. My family needs me to secure our northern border. The armies of Oyo are encroaching on our lands."

"Well, don't let me keep you. Now, let's find out about the wards on Diagon Alley."

Two days with ward picks and detection spells showed that _almost_ all the wards around Diagon Alley were Crawley-isomorphic, and Omoye's silver tongue convinced the few others to switch their wards to match. That done, they carved another plinth, charged it up, and handed it over to the Magic Reversal Squad. And they were happy.

For all of a week.

Hogwarts classes started the next week.

Hogwarts, oddly enough, was warded before any Crawley series wards were invented. The Magic Reversal Squad was not amused. Fortunately, it was a simple operation to add a no-op Crawley field around the castle – during which the second plinth sat in Melina's office, emitting a piercing whistle several thousand times a day. Silencing charms shorted out the map projection, then failed, turning her office into the disco rave from hell – five centuries before they'd invented disco _or_ raves. Fortunately, a quick _reducto_ served as an improvised silencing charm.

Having installed the new wards at Hogwarts (and saying hello to Omoye), Melina crafted a new rune plinth and dropped it off with the Magic Reversal Squad. Finally, time for something more important! She started off on an update on the portkey tracking systems already in place on the island.

Winter saw a fair amount of progress on the portkey trackers. It also, with the Hogwarts holidays, brought The Trace stone back to her office, with a note on it: "Lord Peverell, having grandchildren in Hogwarts, is not a child." Back to the drawing board _again_.

"Okay," she told herself after poring over her old notes, "I wasn't actually detecting magic _by_ an underage mage. I was detecting wand magic _near_ an underage mage." After a good six hours with Whelmsby's _Modern Enchanting_ and de Aquelia's _De Veneficio Stativo_ , she determined that it was effectively impossible to distinguish who had cast a spell.

"So I was doing the right thing, mostly. I just have to make an exception. Find wand magic, see if there's an underage mage around, see if there's no of-age mages close by, and _then_ alert." She nodded to herself.

It only took a couple weeks to get that working – and tested, with the help of more students – and then the newly improved Trace stone was installed in the Magic Reversal Squad room. Melina had peace all the way until summer.

In early July, a note appeared on her desk: "The Trace needs names." Well, it was too much to hope that the work on the Trace was over. Fortunately, there was just a bit of work with Elpheba's Nomenclature Series to get the thing to spit out the names it found. On the plus side, the revised Trace was ready in three days. There was a bug that caused it to spit out all the names related to any incident of wand magic near an underage person, but it wasn't alerting on adults, and she managed to get it to record those in a distinct color. Good enough.

And all was well with the world until Christmas-time. Omoye had owled; she'd managed to set stronger wards on the northern borders of Benin than Melina even thought possible, and with that secured, she was looking at a fast transit system based on Atanwe's Principle of Conjugation.

Just then, Lothian from the Magic Reversal Squad popped in again, a question on his lips.

"If you're here to tell me the Trace is catching house elf magic or something inane like that," she growled as soon as he appeared, "I'm going to fucking stab you with my number three chisel."

He ran.


End file.
